U.S. patent application number 12/889013 was filed with the patent office on 2011-03-24 for underwater compressed fluid energy storage system.
Invention is credited to Scott Raymond Frazier, Brian Von Herzen.
Application Number | 20110070032 12/889013 |
Document ID | / |
Family ID | 43756748 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110070032 |
Kind Code |
A1 |
Frazier; Scott Raymond ; et
al. |
March 24, 2011 |
UNDERWATER COMPRESSED FLUID ENERGY STORAGE SYSTEM
Abstract
A compressed fluid storage system includes a bi-directional
compressor/expander (C/E) unit constructed to compress fluid during
a first operational mode and allow expansion of fluid in a second
operational mode, a fluid storage system positioned on a sea floor
under a body of water, and a piping system positioned between the
C/E unit and the fluid storage system and configured to pass fluid
between the C/E unit and the fluid storage system.
Inventors: |
Frazier; Scott Raymond;
(Golden, CO) ; Von Herzen; Brian; (Minden,
NV) |
Family ID: |
43756748 |
Appl. No.: |
12/889013 |
Filed: |
September 23, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61245279 |
Sep 23, 2009 |
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61309415 |
Mar 1, 2010 |
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61364364 |
Jul 14, 2010 |
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61364368 |
Jul 14, 2010 |
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Current U.S.
Class: |
405/210 |
Current CPC
Class: |
Y02E 60/16 20130101;
Y02E 10/30 20130101; E02D 29/10 20130101; Y02E 10/38 20130101 |
Class at
Publication: |
405/210 |
International
Class: |
B65D 88/78 20060101
B65D088/78 |
Claims
1. A compressed fluid storage system comprising: a bi-directional
compressor/expander (C/E) unit constructed to compress fluid during
a first operational mode and allow expansion of fluid in a second
operational mode; a fluid storage system positioned on a sea floor
under a body of water; and a piping system positioned between the
C/E unit and the fluid storage system and configured to pass fluid
between the C/E unit and the fluid storage system.
2. The system of claim 1 wherein the first and second operational
modes include rotation of a shaft of the C/E unit that is in the
same rotational direction.
3. The system of claim 1 wherein the first operational mode
includes rotation of a shaft of the C/E unit that is in a first
rotational direction, and the second operational mode includes
rotation of the shaft of the C/E unit that is in a second
rotational direction that is opposite the first rotational
direction.
4. The system of claim 1 wherein the C/E unit is positioned on a
platform that is attached to the sea floor.
5. The system of claim 1 wherein the fluid storage system comprises
one or more flexible bags configured to receive pressurized fluid
via the piping system and pressurize the flexible bag against
surrounding water.
6. The system of claim 1 the C/E unit includes a rotating component
configured to rotate in a first rotational direction during the
first operational mode and to rotate in a second rotational
direction during the second operational mode.
7. The system of claim 6 wherein the piping system comprises one of
a rigid pipe, a flexible hose, and a combination thereof.
8. The system of claim 1 wherein the C/E unit is configured to
operate at a pressure that corresponds to a pressure associated
with a depth of the fluid storage system from sea level.
9. The system of claim 1 comprising a generator coupled to the C/E
unit via a clutch, wherein the generator is configured to output
electrical power to an electrical grid when the generator is
coupled to the C/E unit via the clutch.
10. The system of claim 9 comprising a power source coupled to the
C/E unit via a clutch.
11. The system of claim 1 comprising a heat exchanger coupled to
the C/E unit, the heat exchanger configured to pump water thereto
from the body of water during operation.
12. The system of claim 11 further comprising heat exchanger feed
lines configured to selectively draw water from proximate a surface
of the body of water and from proximate the sea floor.
13. The system of claim 12, wherein the surface water is at a first
temperature and the water proximate the sea floor is at a second
temperature that is different from the first temperature, the lower
temperature water being used by the heat exchanger to the C/E in
the first operational mode, and the higher temperature is used by
the heat exchanger to the C/E in the second operational mode.
14. The system of claim 1 wherein the C/E unit is capable of
generating between 0.2 MW and 3 MW of power.
15. The system of claim 1 wherein the C/E unit operates as a
positive displacement unit.
16. The system of claim 1 comprising a power input device coupled
to the C/E unit, the power input device configured to receive power
from one of a wind generator, a Salter duck, a current power
generator, and a tidal power generator.
17. A method of using a compressed fluid storage system, the method
comprising: applying rotational power to a shaft of a pressure
conversion device in a first rotational direction to compress fluid
in a first flow direction through the pressure conversion device;
storing the compressed fluid in a fluid storage system that is
positioned beneath a surface of a body of water; and passing the
compressed fluid from the fluid storage system through the pressure
conversion device in a second flow direction to apply rotational
power to the shaft in a second rotational direction; wherein the
second flow direction is opposite the first flow direction.
18. The method of claim 17 wherein the first rotational direction
and the second rotational direction are the same.
19. The method of claim 17 wherein the second rotational direction
is opposite the first rotational direction.
20. The method of claim 17 comprising extracting power from the
shaft by expanding the compressed fluid in the pressure conversion
device.
21. The method of claim 17 wherein conveying the compressed fluid
to the fluid storage system comprises conveying the compressed
fluid to an isobaric fluid storage system.
22. The method of claim 17 wherein conveying the compressed fluid
comprises conveying the compressed fluid via one of a rigid pipe, a
flexible hose, and a combination thereof.
23. The method of claim 17 comprising engaging the shaft to a
generator via a clutch to extract the power therefrom as electrical
power via the generator.
24. The method of claim 17 comprising positioning the fluid storage
system on a sea floor and at a benthic depth within the body of
water.
25. The method of claim 17 comprising generating the power that is
applied to the shaft via one of a wind generator, a Salter duck, a
wave generator, a current power generator, an ocean thermal energy
converter, and a tidal power generator.
26. A compressed fluid storage system comprising: a power source; a
unitary compressor/expander (C/E) device capable of both
compressing and expanding fluid coupled to the power source via a
shaft and comprising a plurality of compression/expansion (C/E)
stages that pressurize fluid in a compression mode and expand fluid
in an expansion mode; a fluid bag coupled to the plurality of
compression/expansion stages of the unitary C/E device and
positioned under a body of water; a pressured-fluid conveyance
system configured to pass pressurized fluid from the unitary C/E
device to the fluid bag when the unitary C/E device is in the
compression mode, and configured to pass the pressurized fluid from
the fluid bag to the unitary C/E device when the unitary C/E device
is in the expansion mode; and a control unit configured to: invoke
the compression mode in the unitary C/E device, pressurize fluid
and direct the pressurized fluid to pass from the plurality of C/E
stages of the unitary C/E device to the fluid bag when power is
available from the power source; and invoke the expansion mode in
the unitary C/E device, direct the pressurized fluid to pass from
the fluid bag to the plurality of compression/expansion stages of
the unitary C/E device and expand the pressurized fluid when power
is selectively desired to be drawn from the fluid bag.
27. The system of claim 26 comprising a sediment ballast positioned
within the fluid bag.
28. The system of claim 26 wherein the unitary C/E device has a
power capability of between 0.2 MW and 3 MW.
29. The system of claim 26 wherein the unitary C/E device is
configured to operate at a pressure ratio that corresponds to a
water pressure at the depth of the fluid bag within the body of
water and an ambient fluid pressure.
30. The system of claim 26 comprising: a generator to convert
mechanical power to electrical power; and a clutch for coupling the
unitary C/E to the generator; wherein the control unit is
configured to couple the generator to the unitary C/E device via
the clutch when the power is desired to be drawn from the fluid
bag.
31. The system of claim 26 wherein the power source is one of a
wind generator, a Salter duck, a wave generator, a current power
generator, an ocean thermal energy converter, and a tidal power
generator.
32. The system of claim 26 comprising a heat exchanger coupled to
the unitary C/E device and configured to draw water from the body
of water to: cool the C/E device when the fluid is pressurized; and
warm the C/E device with the pressurized fluid is expanded.
33. The system of claim 32 further comprising heat exchanger feed
lines connecting the heat exchanger to the C/E unit and configured
to selectively draw water from proximate a surface of the body of
water and from proximate the sea floor.
34. The system of claim 33, wherein the surface water is at a first
temperature and the water proximate the sea floor is at a second
temperature that is different from the first temperature, the lower
temperature water being used to cool the fluid in the C/E in
compression mode, and the higher temperature is used to heat the
fluid in the C/E in expansion mode.
35. The system of claim 26, wherein the compression mode comprises
rotation in one direction, and the expansion mode comprises
rotation in the other direction.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority to U.S. Provisional
Application 61/245,279 filed Sep. 23, 2009, to U.S. Provisional
Application 61/309,415 filed Mar. 1, 2010, to U.S. Provisional
Application 61/364,364 filed Jul. 14, 2010, and to U.S. Provisional
Application 61/364,368 filed Jul. 14, 2010, the disclosures of
which are incorporated herein.
BACKGROUND OF THE INVENTION
[0002] Embodiments of the invention relate generally to compressed
fluid energy storage and, more particularly, to a method and
apparatus of storing compressed fluid in an underwater storage
device and extracting energy therefrom. In embodiments where the
fluid compressed is air, such inventions are part of a class of
energy storage systems known as compressed air energy storage
(CAES) systems, but in this document we will use CAES to refer
generically to any compressed fluid energy storage system.
[0003] Renewable energy (RE) sources offer an alternative to
conventional power sources in an age of dwindling non-renewable
energy sources and high carbon emissions. However, RE sources are
often not fully exploited because many forms of renewable energy
are not available when the peak demand is present. For instance, RE
sources may be most available during undesirable off-peak hours, or
may be located in areas that are remote from population centers or
locations where power is most needed, having to share the grid
during peak hours along with all the other peak power sources.
[0004] RE sources may include hydro power, geothermal, Ocean
Thermal Energy Conversion (OTEC), as examples. Hydro power, for
instance, when combined with a reservoir is one RE source that can
be throttled up and down to match or load-follow the varying power
loads. Geothermal and OTEC are also good baseload RE resources;
however, locations viable for their use tend to be limited. It is
to be understood that an ocean thermal energy converter, while
traditionally utilized across the thermocline of an ocean, can
additionally apply to fresh bodies of water that have a temperature
difference between surface water and deep water. RE sources may
also include solar, wind, wave, and tidal, as examples. However
these sources tend to be intermittent in their ability to provide
power. Energy storage is thus desired for those sources to
substantially contribute to the grid energy supply.
[0005] For instance, wind energy may be cost effective on a cost
per kWh but does not may not produce energy when it's needed. It
faces impediments to even modest grid penetration levels largely
due to the timing of its power output, which is not only not
dispatchable according to the demands of the grid, but it varies
uncontrollably according to wind levels. This problem will get
worse as more RE sources of all kinds are added to the grid--as
long as cost effective storage is unavailable. Above 20% renewable
energy fraction, electrical power grids often lose stability
without energy storage to modulate energy supply and demand.
[0006] Cost-effective storage for the electrical grid has been
sought from the beginning of electrical service delivery but is not
yet available. The variation in power demand throughout a day, and
season-to-season, requires having generation assets that are
utilized only part of the time, which can increase capital,
operations, and maintenance costs for assets used at less than full
capacity. Also some generation assets are difficult to throttle or
shut down and are difficult to return to full power in short
periods of time. Energy storage can provide a buffer to better
match power demand and supply allowing power sources to operate at
higher capacity and thus higher efficiency.
[0007] Cost parameters of several leading storage technologies may
be considered for large scale energy systems and each technology
has its own cost drivers. Pumped hydroelectric, for example, has
been used for many decades and is often considered the standard by
which other grid energy storage ideas are judged. It is efficient
from an energy capacity standpoint, consumes no fuel upon
harvesting the stored energy, but can only be deployed in limited
locations and has high capital cost per unit power. A substantial
elevation change and two reservoirs are typically required. Also,
most of the viable sites in North America are considered to be
already developed, so, regardless of cost, it does not appear that
pumped hydroelectric will be able to contribute much additional
energy storage capacity. It is also fairly expensive in terms of
power cost ($/kW) but nonetheless is widely used when available due
to fairly inexpensive cost per unit energy ($/kWh).
[0008] CAES is an attractive energy storage technology that
overcomes many drawbacks of known energy storage technologies. A
conventional approach for CAES is to use a customized gas turbine
power plant to drive a compressor and to store the compressed air
underground in a cavern or aquifer. The energy is harvested by
injecting the compressed air into the turbine system downstream of
the compressor where it is mixed with, or heated by natural
gas-fired combustion air and expanded through the turbine. The
system operates at high pressure to take advantage of the modest
volume of the cavern or aquifer. The result is a system that
operates with constant volume and variable pressure during the
storage and retrieval process, which results in extra costs for the
compressor and turbine system because of the need to operate over
such a wide range of pressures. Underground CAES suffers from
geographic constraints. Caverns may not be located near power
sources, points of load or grid transmission lines. In contrast,
over 90% of the electrical load in the industrialized world lies
within reach of water deep enough for underwater CAES to be
practical. Underwater CAES removes many of the geographic
constraints experienced by underground CAES.
[0009] Also, an important factor for efficient compression and
expansion of a fluid is dealing with the heat generated during
compression and the heat required during expansion. Conventional
CAES reheats air using combustion of natural gas (often by
absorbing heat from the gas turbine exhaust) and gives up the heat
of compression to the ambient environment. Such systems can include
a thermal storage device to enable adiabatic operation. Such
systems also often have separate equipment for compression and
expansion phases, and therefore have a greater capital expense, as
well as higher operating cost and complexity due to the use of
natural gas. The result is that the power plant, when utilizing
purchased off-peak power to charge the air reservoir can generate
power during periods of peak demand, but with additional equipment
and higher fuel costs.
[0010] Therefore, it would be desirable to design an apparatus and
method of storing and recovering energy in a compressed fluid
energy storage system in a more efficient and cost-effective
manner, without need for external fuel, that is competitive with
conventional power sources.
BRIEF DESCRIPTION
[0011] According to one aspect of the invention, a compressed fluid
storage system includes a bi-directional compressor/expander (C/E)
unit constructed to compress fluid during a first operational mode
and allow expansion of fluid in a second operational mode, a fluid
storage system positioned on a sea floor under a body of water, and
a piping system positioned between the C/E unit and the fluid
storage system and configured to pass fluid between the C/E unit
and the fluid storage system.
[0012] According to another aspect of the invention, a method of
using a compressed fluid storage system, the method includes
applying rotational power to a shaft of a pressure conversion
device in a first rotational direction to compress fluid in a first
flow direction through the pressure conversion device, storing the
compressed fluid in a fluid storage system that is positioned
beneath a surface of a body of water, and passing the compressed
fluid from the fluid storage system through the pressure conversion
device in a second flow direction to apply rotational power to the
shaft in a second rotational direction, wherein the second flow
direction is opposite the first flow direction.
[0013] According to yet another aspect of the invention, a
compressed fluid storage system includes a power source, a unitary
compressor/expander (C/E) device capable of both compressing and
expanding fluid coupled to the power source via a shaft and
comprising a plurality of compression/expansion (C/E) stages that
pressurize fluid in a compression mode and expand fluid in an
expansion mode, a fluid bag coupled to the plurality of
compression/expansion stages of the unitary C/E device and
positioned under a body of water, a pressured-fluid conveyance
system configured to pass pressurized fluid from the unitary C/E
device to the fluid bag when the unitary C/E device is in the
compression mode, and configured to pass the pressurized fluid from
the fluid bag to the unitary C/E device when the unitary C/E device
is in the expansion mode, and a control unit configured to invoke
the compression mode in the unitary C/E device, pressurize fluid
and direct the pressurized fluid to pass from the plurality of C/E
stages of the unitary C/E device to the fluid bag when power is
available from the power source, and invoke the expansion mode in
the unitary C/E device, direct the pressurized fluid to pass from
the fluid bag to the plurality of compression/expansion stages of
the unitary C/E device and expand the pressurized fluid when power
is selectively desired to be drawn from the fluid bag.
[0014] Various other features and advantages will be made apparent
from the following detailed description and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The drawings illustrate one preferred embodiment presently
contemplated for carrying out the invention.
[0016] In the drawings:
[0017] FIG. 1 is a schematic diagram illustrating general
functionality of embodiments of embodiments of the invention.
[0018] FIG. 2 is a schematic diagram illustrating a system having
the functionality illustrated in FIG. 1 according to embodiments of
the invention.
[0019] FIG. 3 is a schematic diagram illustrating basic components
of a system positioned at sea according to an embodiment of the
invention.
[0020] FIG. 4 is a schematic diagram illustrating basic components
of a system positioned on land according to an embodiment of the
invention.
[0021] FIG. 5 is a schematic diagram illustrating differences
between adiabatic and isothermal operation.
[0022] FIG. 6 illustrates a rotary Wankel compressor/expander
(C/E).
[0023] FIG. 7 illustrates a system having a clutch and heat
exchanger according to an embodiment of the invention.
DETAILED DESCRIPTION
[0024] Embodiments of the invention include deployment or
installation of compressed fluid storage vessels on a floor of an
ocean, sea, lake, reservoir, gulf, harbor, inlet, river, or any
other manmade or natural body of water. As used herein, "sea"
refers to any such body of water, and "sea floor" refers to the
floor thereof "Fluid," as used herein, refers to any compressible
gas or liquid such as air, CO2, or the like as well as to a
supercritical fluid. "Sediment" (e.g., "sea floor sediment"), as
used herein, refers to marine material from the bottom or sea floor
of the sea and may include, by way of example, gravel, sand, silt,
clay, mud, organic or other material settled onto the floor of the
sea.
[0025] In disclosed embodiments of the system, compressed fluid is
stored in a bag in (or referred to as `under`) a body of water.
Hydrostatic pressure of surrounding water becomes the predominant
restraining parameter for the compressed fluid, which is
pressurized into the bag via a compressor. In traditional "pumped
hydro" storage, water is pumped through a substantial geographic
elevation. In contrast, in embodiments of the disclosed system, the
level of a body of water is essentially lifted through the
mechanism of adding fluid below it. The technology applies equally
well to an ocean or an inland lake or reservoir. The disclosed
system often operates at lower pressure ratios than traditional
CAES (based on the depth of the water), and these lower pressure
ratios and use of the water as a vast heat sink, in several
embodiments as will be discussed, eliminates the need for fossil
fuels to reheat the fluid immediately prior to or during the
expansion phase. Also, the system operates with a nearly constant
storage pressure allowing simpler and more efficient
compressor/expander (C/E) designs.
[0026] Referring now to FIG. 1, a general functionality of
embodiments of the disclosed system is illustrated. System 10
includes input power 12 which can be, in embodiments of the
invention, from a renewable energy source such as wind power, wave
power (e.g., via a "Salter Duck"), current power, tidal power, or
solar power, as examples. In another embodiment, input power 12 may
be from an electrical power grid. In the case of a renewable energy
(RE) source, such a source may provide intermittent power. In the
case of an electrical power grid, system 10 may be connected
thereto and controlled in a fashion that electrical power may be
drawn and stored as compressed fluid energy during off-peak hours
such as during late evening or early morning hours, and then
recovered during peak hours when energy drawn from system 10 may be
sold at a premium (i.e., electrical energy arbitrage), or to
augment base load power systems such as coal to provide peaking
capability by storing inexpensive base load power. Another way of
operating would be to use system 10 as a base power supply to
provide low-cost power therefrom in a generally static mode in lieu
of a conventional power source such as coal, and use conventional
power sources (e.g., natural gas, diesel, etc. . . . ) as peak
power systems to provide transient power as the load fluctuates and
exceeds the supply from system 10, thus reducing the average cost
of power.
[0027] Also, system 10 is not limited to the aforementioned power
sources, but applicable to any power source, including
intermittently available power sources, or sources from which may
be drawn during low-cost or off-peak hours and sold during a period
that is desirable, such as during a peak electrical load or
generating-plant outage. Further, system 10 is not limited to a
single input power 12 but may include multiple sources which may be
coupled thereto. In other words, multiple and combined power
sources may be included in a single system as input power 12. Input
power 12 is coupled to mechanical power 14 to compress fluid from a
fluid inlet 16.
[0028] Fluid compression 18 may be from a device that can both
compress and expand a fluid, depending on direction of rotation,
such as a Wankel-type compressor/expander (C/E). However, the
invention is not so limited, and any compressor that uses
mechanical power to compress a fluid may be implemented according
to embodiments of the invention, and any expander that decompresses
a fluid to generate mechanical energy may be implemented according
to embodiments of the invention. In embodiments of the invention
the C/E is capable of generating between 0.2 MW and 3 MW of power;
however, the invention is not so limited and may be capable of
generating any range of power commensurate with system requirements
that may include a power as low as 0.0001 MW and a power as high as
5 MW or greater. Thus, fluid compression 18 occurs as a result of
mechanical power 14 using fluid input 16. Fluid compression 18 may
occur in one or multiple cycles, and cooling may be introduced via
pumps and heat exchangers, between stages, as is known in the art.
Cooling may also be achieved through direct contact between the
compressed fluid and a cooling fluid. Fluid from fluid compression
18 is conveyed to compressed fluid storage 20 via a fluid input 22.
Also, compressed fluid storage 20 may be a bag or other conformal
fluid containment device that may be ballasted within a body of
water such as a lake, reservoir (natural or man-made), or sea,
using sediment as ballast, and at a depth to which fluid may be
compressed and stored for later extraction. As such, the volume of
fluid is stored nearly isobarically as a function of the amount of
fluid therein and as a function of its depth within the body of
water.
[0029] The fluid storage bags or tubes may be rated to 50.degree.
C. In one compressor design according to an embodiment of the
invention, where the heat of compression is recovered and stored,
the expected exit temperature of the fluid from the expander into
the fluid hose is only about 5.5.degree. C. above the water
temperature. Where only ambient water is used to cool the
compression stages and there is no heat exchanger after the final
stage, the temperature of the fluid into the fluid hose may be
30.degree. C. above ambient, or 45.degree. C. in the case of a
15.degree. C. surface ocean temperature. If the tube temperature
limit is exceeded for any reason, a temperature alarm can shut down
the compressor. One or more temperature sensors may be positioned
along the length of a fluid storage tube in a CAES system such that
the temperature of the fluid storage tube may be monitored. For
example, a temperature alarm may indicate to a system operator that
a temperature limit has been reached or exceeded. In addition, an
alarm shutdown on the system compressor may cause the compressor to
stop supplying compressed fluid to the affected fluid tube to
lessen or prevent damage to the fluid storage tube or to the fluid
hose connected to the affected fluid storage tube. The bag
experiences constant pressure due to the variable-volume design and
thus no additional heating occurs within the bag.
[0030] When it is desirable to draw stored energy from system 10,
compressed fluid may be drawn from compressed fluid storage 20 via
fluid output 24 and fluid expansion 26 occurs. As known in the art,
fluid expansion 26 results in available energy that may be conveyed
to, for instance, a mechanical device, which may extract mechanical
power 28 for electrical power generation 30, which may be conveyed
to a grid or other device where it is desirable to have electrical
power delivered. Outlet fluid 32 is expelled to the environment at
generally standard or ambient pressure. In embodiments of the
invention, mechanical power 28 may be produced from, as an example,
a Wankel-type expander. Further, as will be discussed, mechanical
power 14 for fluid compression 18 and mechanical power 28 derived
from fluid expansion 26 may be via the same device (i.e., a
compression/expansion or "C/E" device) or via a different or
separate device within system 10.
[0031] In principle, a C/E may be used in an isothermal operation,
an adiabatic operation, or a combination thereof. In another
example, a C/E may be implemented that does not use a distinct heat
exchanger and does not use a thermal reservoir. As is known in the
art, when a fluid is compressed, it heats, and when a fluid is
expanded, it cools. As such, embodiments of the invention include
forced-convection cooling 34 to cool the fluid from fluid
compression 18 and forced-convection heating 36 to heat the fluid
from fluid expansion 26. Because fluid storage occurs at generally
ambient temperature and pressure (i.e., at depth within the body of
water as discussed), both cooling 34 for fluid compression 18 and
heating 36 after fluid expansion 26 may be performed using the vast
amount of fluid that surrounds system 10 (i.e., lake or seawater).
As such, system 10 may be operated, in some embodiments, in a
generally isothermal manner that cools the fluid to near ambient
during compression stage(s) and heats the fluid to near ambient
during expansion stage(s). In other embodiments, system 10 may be
operated in a generally adiabatic manner where energy from
compression is stored via a controlled heat transfer process to a
thermal storage tank, and energy to heat the fluid after expansion
is likewise drawn from the energy stored in the storage tank,
having relatively little heat exchange with the surrounding
environment. In such fashion, the system includes a way to modulate
or recover the sensible heat in the compressed fluid. However, in
either case, pumps and heat exchangers may be employed to cool at
desired locations in the system, as understood in the art.
[0032] In yet another embodiment, energy from fluid compression 18
is not stored per se, but water is selectively drawn into system 10
by taking advantage of the natural temperature difference between
the surface water temperature and the temperature in the depths. In
such an embodiment, cooling 34 during fluid compression 18 may be
performed using relatively cold water obtained from the depths
(i.e., well below water surface), and heating 36 during fluid
expansion 26 may be performed using relatively warm water obtained
from near the water surface. Utilizing this temperature difference
in this manner is actually adding a heat engine cycle on top of the
energy storage cycle, thus making it conceivable that more energy
would be extracted than was stored, due to the thermal energy input
of the water body.
[0033] System 10 includes a controller or computer 38 which may be
controllably linked to components of system 10.
[0034] Referring now to FIG. 2, multiple systems such as system 10
of FIG. 1 may be deployed according to an embodiment of the
invention. As will be described in further detail with respect to
additional figures below, each system 10 may include a unitary or
bi-directional compressor/expander (C/E) unit that is coupled to a
fluid storage tube assembly that is positioned well below the
surface of a water body. Each C/E is coupled to an energy source
and a generator. The energy source may be a renewable source such
as wind or wave power, or it may be from the generator itself,
which is caused to operate as a motor having energy drawn from a
power grid or from a renewable source such as a solar photovoltaic
array.
[0035] Thus, FIG. 2 illustrates an overall system 50 having a
plurality of systems 10 as illustrated in FIG. 1 and in subsequent
figures and illustrations. Each system 10 includes a C/E 52
configured having a power input 54 and also coupled to a generator
56 (or motor/generator). Each generator 56 is configured having a
respective power output 58. In one embodiment, each power output 58
is coupled separately to a load or utility grid; however, in
another embodiment as illustrated, multiple power outputs 58 from
two or more generators 56 may be combined to output a combined
power output 60 to a load or utility grid.
[0036] Each C/E 52 is coupled to a fluid storage tube assembly 62,
which, as will be further discussed, is positioned at depth and is
configured to receive compressed fluid from a respective C/E 52.
According to embodiments of the invention, each C/E 52 may be
coupled to multiple fluid storage tube assemblies 62 via a tube or
pipe 64. As such, a single C/E 52 may be coupled to a vast number
of fluid-storage assemblies 62 and may be limited by the number of
feed lines and the terrain on which the fluid storage tube
assemblies 62 are positioned, as examples. Operation of overall
system 50 may be controlled via a computer or controller 66, and
one skilled in the art will recognize that each system 10 may
include control valves, pressure sensors, temperature sensors, and
the like, distributed throughout. Controller 66 is configured to
pressurize fluid and direct the pressurized fluid to pass from C/E
52 or stages thereof to fluid storage tube assemblies 62 when power
is available from the power source, and direct the pressurized
fluid to pass from fluid storage tube assemblies 62 to C/E 52 or
stages thereof and expand the pressurized fluid when power is
selectively desired to be drawn from fluid storage tube assemblies
62.
[0037] As such, overall system 50 may be deployed in a modular
fashion having multiple systems 10 (only two of which are
illustrated in FIG. 2). Accordingly, this modularity provides
system resilience and an ability to swap units in the field with
minimum overall system downtime by allowing a portion of the system
to be taken offline while the rest of the system continues to
operate. Modularity also enables separate systems to operate
simultaneously in different modes (i.e., one system collects/stores
energy while another generates power). Thus, multiple CEs may be
ganged together, as illustrated in FIG. 2, enabling modularity.
And, each system 10 may be controlled in a fashion where, for
instance, an individual fluid storage tube assembly 62 may be
decoupled or isolated from its respective C/E 52. Accordingly,
during operation, individual systems 10 or components of an
individual and specific system 10 may be removed from service for
trouble-shooting, repair, or routine maintenance. Thus, the
modularity provides ease of servicing that enhances overall
reliability, since the overall system 50 would not need to be shut
down for servicing.
[0038] Further, because of the modularity of overall system 50,
additional systems 10 may be added incrementally thereto, or
additional storage may be added to each system 10 during operation.
Thus, as power demands change over time (i.e., population growth or
decrease in a given service area), power and/or storage capacity
may be added or removed in a modular fashion consistent with that
illustrated in FIG. 2, over time and in concert with changing
system requirements. Thus, a modular system is expandable and other
systems may be constructed and brought online with minimal impact
to overall system downtime and operation.
[0039] Additionally, systems 10 of overall system 50 may be
operated in separate fashions from one another simultaneously. For
instance, in one portion of an array of systems 10, one of the
systems 10 may be exposed to a high wind and thus operated in
compression mode to store energy therefrom in its respective fluid
storage tube assembly 62. However, at the same time, another one of
the systems 10 may be in an area receiving little or no wind and
thus operated in expansion mode to draw energy from its respective
fluid storage tube assembly 62.
[0040] As such, overall system 50 may be operated in a flexible
fashion that allows multiple modes of operation, and also may be
configured in a modular fashion to allow portions thereof to be
temporarily shut down for maintenance, repair, and operation, or
permanently decommissioned, without having to shut down the overall
system 50.
[0041] Further, configuration and operation of overall system 50 is
in no way limited to the examples given. For instance, instead of
wind energy, systems 10 may be coupled to a wave energy source or a
water current source, as further examples. Systems 10 may each
employ multiple C/Es 52, or C/Es 52 may be configured to share
fluid storage therebetween. Thus, in one example, an auxiliary feed
line 68 may be positioned and configured to separately couple one
C/E 70 of one system 10 with fluid storage tube assemblies 72 of
another system. In such fashion, storage capacity of fluid storage
tube assemblies 72 may be used during, for instance, repair or
maintenance of one C/E 70. In addition, rerouting, an example of
which is shown in feed line 68, enables the cooperative use of
multiple C/E's 52 and 70 to additional advantage, including
modularity, system resilience, incremental expandability of power
capacity, field-swappability of C/E units, and the ability to
operate one C/E in compression mode and another C/E in expansion
mode. These advantages result in a system with graceful
degradation, no single point of failure of the entire system, and
flexibility to add capability as power and storage requirements
increase. It also enables a flow-through mode of operation where
power from a prime mover (such as a wind generator, a wave power
generator (e.g., via a "Salter Duck"), a current power generator, a
tidal power generator, and an ocean thermal energy converter, as
examples) passes through a first C/E, compressing fluid, is
optionally stored, and passes through a second C/E in expansion
mode, generating power for the grid. Such an embodiment eliminates
ramp/up and ramp/down time for the system, enabling a standby mode
of operation that is ready to absorb power or deliver it on demand
without delay.
[0042] Referring now to FIG. 3, basic components of system 10
positioned at sea are illustrated. Components of system 10 may be
positioned on a platform 98 proximately to the water surface. Thus,
FIG. 3 illustrates a sea 100 and a sea floor 102. Sea 100 includes
an ocean, a lake, or a reservoir such as in a dammed river, and in
this and all embodiments is not limited to any specific body of
water. System 10 includes a flexible fluid bag or fluid bag
assembly 104 positioned at an average depth 106, a unidirectional
or bi-directional fluid pressure conversion device or
compressor/expander (C/E) 108 coupled to a generator 110, and a
heat transfer system (pumps and heat exchangers as discussed with
respect to FIG. 1, not illustrated). C/E 108 may include multiple
stages of compression and expansion, and a heat exchanger package
(not shown) may cool or reheat the fluid between the stages of
compression or expansion, respectively. The tubes carrying the
pressurized fluid are immersed in circulating water, or more
commonly, the pressurized fluid is passed over a finned tube heat
exchanger inside which flows inside the finned tubes. System 10 may
be configured to operate substantially in nearly-isothermal or
adiabatic modes.
[0043] One skilled in the art will recognize that system 10 of FIG.
3 may include but is not limited to other devices such as a control
system, a computer, and one or more clutches to mechanically couple
components thereof. The bag 104 is ballasted so it doesn't float to
the surface when inflated.
[0044] A fluid hose or pipe, or pressurized-fluid conveyance system
112 connects fluid storage bag assembly 104 with the C/E 108 at or
near the surface of sea 100. The C/E 108 is coupled to generator
110, which in one embodiment is the same generator used by a wind
turbine, with a clutch (shown in FIG. 4). The generator 110 can act
as a motor as well to drive the C/E 108 in compressor mode when
storing energy, or if the wind is blowing, the wind power can be
put into the generator 110. Thus, when full power from the system
is desired, for example during peak demand periods on the grid, the
stored fluid expanding through the C/E 108 augments the torque to
the generator 110. In embodiments, generator 110 is an (alternating
current) A/C generator, and in other embodiments, generator 110 is
a (direct current) DC generator.
[0045] DC power transmission is not often used for land-based
transmission because of the cost of conversion stations between
transmission lines. However, the efficiency of DC transmission
lines can be greater than A/C lines, particularly under salt water.
Other advantages of DC power transmission include a clearer power
flow analysis and no requirement to synchronize between independent
grid sections connected by the DC line. Additional benefits of DC
transmission may be realized when the lines are run underwater due
to capacitance of the transmission line. Thus, many DC transmission
systems are in existence today.
[0046] C/E 108 provides the ability to both compress and expand
fluid. In one embodiment, C/E 108 is a single component that
includes the ability to compress fluid when work is input thereto
and to expand fluid to extract work therefrom. In such an
embodiment, a single fluid hose or pipe 112 is positioned between
fluid storage tube assembly 104 and C/E 108, and fluid is pumped to
and from fluid storage tube assembly 104 using fluid hose or pipe
112. Thus, when power is input 114 to C/E 108, C/E 108 operates to
compress fluid, convey it to fluid storage tube assembly 104 via
fluid hose or pipe 112, and store the energy therein. Power 114 may
be provided via a renewable source such as wind, wave motion, tidal
motion, or may be provided via the generator 110 operated as a
motor which may draw energy from, for instance, a power grid. Also,
C/E 108 may be operated in reverse by drawing compressed stored
energy from fluid storage tube assembly 104 via fluid hose or pipe
112. Thus, by reversing its motion, C/E 108 may be caused to
alternatively compress or expand fluid based on a direction of
operation or rotation. Note that the generator 110 provides
electrical power in one embodiment. Alternatively, mechanical power
may be utilized directly from the expander without the use of
generator 110.
[0047] However, in another embodiment, compressor and expander
functionalities of C/E 108 are separated. In this embodiment, an
expander 116 is coupled to fluid storage tube assembly 104 via
fluid hose or pipe 112, and a compressor 118 is coupled to fluid
storage tube assembly 104 via the same fluid hose 112, or,
alternatively, a separate fluid hose, pipe, or piping system 120.
Thus, in this embodiment, power may be input 114 to compressor 118
via, for instance, a renewable energy source that may be
intermittent--providing compressed fluid to fluid storage tube
assembly 104 via separate fluid hose or pipe 120. In this
embodiment, energy may be simultaneously drawn from fluid storage
tube assembly 104 via fluid hose or pipe 112 to expander 116. Thus,
while providing the system flexibility to simultaneously store and
draw power, this embodiment does so at the expense of having
separate compressor 118 and expander 116 (additional compressor and
expander not illustrated).
[0048] Referring now to FIG. 4, basic components of system 10
positioned on land are illustrated. Much like system 10 of FIG. 3,
system 10 of FIG. 4 is able to receive power from a grid, from one
or more renewable energy systems, or both. This system is likewise
able to store energy in an underwater isobaric fluid storage bag or
tube assembly that is compressed in a C/E device and to extract the
energy therefrom also via the C/E device. The system may be
configurable to operate in isothermal or adiabatic mode.
[0049] An important factor in whether the fluid passageway from the
surface to the bag should be rigid or flexible is whether the
surface unit is floating or fixed to the sea floor. In deeper
water, many RE harvesting schemes use a floating and anchored base.
So if the wind or wave direction changes, the position of the base
moves until the anchor lines are tensioned in a new direction.
[0050] Rigid fluid pipes are generally less expensive since they
may be simply steel pipes with diameters that are commonly used in
the offshore marine industry. The deployment techniques can be a
bit more involved since field joints (those connected in the field,
not at the manufacturing yard) will be needed for deep or long
pipes. A flexible hose is easier to fabricate completely on shore
and deploys more easily, but it requires a more complicated and
expensive design. Such hoses have a relatively flexible liner that
in one embodiment provides the fluid seal with a braided overwrap
of high strength material like metal or fiberglass to carry the
pressure load. The diameter of these hoses for a 2.5 MW C/E unit (a
size similar to an offshore wind turbine) could be, in one
embodiment, about 28 cm in diameter (11'') for a bag depth of 100 m
and has operating pressures of 1.1 million Pascals (165 PSI).
Offshore platforms deal with floating, moored platforms and "rigid"
connections to the bottom sediments (e.g., drill shafts), so a
flexible hose is not strictly required for such moored platforms.
The deflection strains over the length of the pipe could be well
inside the limits of the pipe's structural capabilities. Also note
that the pressure difference between the fluid inside and the
exterior pressure varies with the depth. Near the bottom of the
pipe/hose the pressure differences are small, which is why a thin
plastic bag can hold the pressurized fluid at the floor, suggesting
hybrid or combination solutions where a flexible and fairly
unreinforced hose can be used near the bag and a rigid, simple pipe
used in the upper sections.
[0051] FIG. 4 illustrates a system 10 where components other than
compressed fluid transmission and storage are located on land 122.
Thus, in this system, capital cost may be reduced by avoiding the
cost related to off-shore setup and operation. However, operational
locations may be more limited, as it may be desirable to operate in
100 feet of water or deeper. Thus, in order to reach such desirable
depths, it may be necessary to convey pressurized fluid over longer
distances. Further, it is often desirable for environmental,
aesthetic, and other reasons to locate RE power systems well away
from populated areas. In addition, renewables such as wind
typically provide much greater power at distances removed from land
shapes and other wind obstructions. As such, FIG. 4 illustrates a
system 10 configured to operate on land according to embodiments of
the invention. System 10 of FIG. 4 may incorporate elements of
FIGS. 1 through 3 as discussed above. In one embodiment,
bi-directional C/E 108 includes a shaft 124 configured to operate
in a first rotational direction 126 to compress fluid in a first
flow direction 128 during a compression phase causing fluid to pass
through fluid hose or pipe 112 to storage. In this embodiment,
shaft 124 of C/E 108 may be caused to operate in a second
rotational direction 130 that is opposite first rotational
direction 126 by expanding fluid from storage and flowing the fluid
through C/E 108 in a second flow direction 132. A clutch 134
couples shaft 124 to generator 110, in this embodiment, to enable
energy extraction from storage via generator 110 and to de-couple
generator 110 when power is input to C/E 108 by a source other than
generator 110. And, although bi-directional operation is
illustrated with respect to FIG. 4, it is to be understood that all
systems disclosed herein may be uni-directionally configured as
well.
[0052] FIG. 5 illustrates differences between adiabatic and
isothermal operation. Isothermal operation typically refers to
operation where a C/E is bathed in a coolant or otherwise cooled
via a pump/heat exchanger during compression and warmed by a
thermal reservoir during expansion steps (such as fluid compression
18 and fluid expansion 26 illustrated in FIG. 1) while adiabatic
operation typically refers to a system having stored energy and
relatively little heat transfer with the surrounding environment,
and energy from fluid compression 18 may be stored in a thermal
storage system. One skilled in the art will recognize that any C/E
capable of both compression and expansion may be operated in an
isothermal fashion, an adiabatic fashion, or in an adiabatic
fashion having intercooling between multiple stages. In such
embodiments, it is possible to cool or warm using a reservoir of
fluid (i.e., a lake or ocean, etc.), or energy may be stored from
the heat of compression and stored for later use to heat the C/E
during expansion. In addition, the C/E may be operated in an
enhanced isothermal mode of operation. It is common for the surface
of a body of water to be at one temperature, while the bottom of a
body of water to be at another temperature. It is possible to
compress using the colder water source and expand using the warmer
water source. In this way, heat energy is extracted from the body
of water and improves the efficiency of the storage device. In
principle, it is possible to extract more energy from the storage
device than was input by the prime mover, because additional
thermal energy is added by the thermal energy transferred from the
body of water to the system, potentially overcoming the system
losses.
[0053] Typically, isothermal operation takes advantage of the vast
reservoir of water in or near which a system will be placed. Thus,
a pump 136 may be positioned to feed water to the
compressor/expander between compression/expansion stages thereof.
However, in an alternate embodiment, adiabatic operation may be
implemented by including a thermal storage tank 138 coupled to the
compressor/expander via pump 136 and configured to extract energy
between stages after compression and to add energy between stages
after expansion. As is known in the art, large cooling tanks may be
operated in such a fashion that thermal stratification occurs
therein; thus, hot water may be fed to and drawn from the top of
thermal storage tank 138, and cold water may be fed to and drawn
from the bottom of thermal storage tank 138. Thus, in one example,
during compression, cold water could be drawn from the bottom
(relatively cold) portion of the tank and returned to the top
(relatively hot). Conversely, during expansion, hot water could be
drawn from the top (relatively hot) portion of the tank and
returned to the bottom (relatively cold). Thus, in both modes of
operation, stable stratification of the thermal storage tank is
achieved, preserving the thermal differences of the water portions
due to low inherent thermal diffusivity of water under stable
conditions.
[0054] In one embodiment and as discussed above, in lieu of a
thermal storage tank, the effect of adiabatic operation may be
realized to an extent by extracting relatively cold water from a
deep sea depth via a cold inlet line or heat exchanger feed line
140, and extracting relatively warm water from near the water
surface via a warm inlet line or heat exchanger feed line 142.
Further, as understood in the art, thermal storage tank 138 may be
positioned on a platform and positioned over the water surface,
immersed in the water itself, installed on the sea floor or lake
floor, or positioned on land (particularly in a land-based system).
Further, in an embodiment where thermal storage tank 138 is
immersed, according to one embodiment, algae and other sea life may
be encouraged to reside on the surface of thermal storage tank 138
in order to enhance the insulating ability thereof.
[0055] Further, one skilled in the art will recognize that power
output such as combined power output 60 of FIG. 2 may be via DC
electrical transmission or A/C electrical transmission. Thus, in
one embodiment, output electrical power is stepped up to a high A/C
voltage and transmitted to a load or grid, while in another
embodiment, a DC voltage is transmitted to a load or grid. As is
understood in the art, A/C typically includes relatively higher
transmission costs but lower capital expense compared with DC.
[0056] As such, embodiments of the disclosed invention include an
improved efficiency over other RE systems such as conventional CAES
due to a lower heat of compression, an approximately isobaric or
constant pressure operation, a decreased temperature and pressure
differentials, and the use of a relatively low speed rotary engine
design. Embodiments of the invention also decrease levelized cost
of energy delivered to the grid by eliminating fuel costs and by
decreasing capital costs of CAES technology.
[0057] Positive displacement machines generally operate at lower
speeds than turbines, leading to fewer tolerance constraints and
hence lower fabrication costs. Typically, positive displacement
machines trap a fixed amount of fluid that is forced into a
discharge pipe. Positive displacement machines also efficiently
scale down in size, leading to machines that can be modular and
flexible when compared to a turbine. As such, capital costs may be
reduced for a positive displacement machine, as turbines tend to be
expensive due to the need to operate at high tangential speeds for
aerodynamic compression and expansion. High turbine speeds also can
create substantial stresses and lubrication challenges,
particularly when operating at higher temperatures during
compression. High speed turbines also typically cannot efficiently
operate in reverse direction to extract work from a high pressure
fluid due to differences in the optimal turbine blade shape in
compression and expansion.
[0058] Thus, a general approach to capital cost reduction is to use
a machine that is both inexpensive and can be used in a compressing
mode when rotated in a first direction during a first operational
cycle (e.g., during storage), and in an expanding mode when rotated
in a second direction that is opposite the first direction during a
second operational cycle (e.g., during energy extraction). However,
some positive displacement machines have a reverse flow direction
without requiring a change in shaft rotation direction. Efficiency
may be increased by using many stages in both compression and
expansion, and ambient temperature water may be employed to keep
temperature changes to a minimum. Positive displacement machines
may be designed to perform both functions (compression and
expansion) well in contrast to a dynamic compressor or turbine.
[0059] Typical internal combustion engines or reciprocating fluid
compressors can efficiently provide both the compression and
expansion functions. Such machines typically have compression
ratios of approximately 4 to 12 per stage, which makes the machine
simple and capable of fairly high pressure ratios with just a few
stages. However, these relatively high pressure ratios can be
inefficient in a C/E application if the high-temperature energy in
the compressed fluid is not captured, efficiently stored and
reused. This issue can be mitigated using interstage coolers.
Minimum compressor input energy and maximum energy recovery occurs
if the fluid temperature does not change much through the process.
Efficient machines cool the fluid between compression stages and
conversely heat it between stages of expansion. Thus, for smaller
pressure changes per stage, it is easier to keep temperature
variations to a minimum, improving efficiency when using a constant
temperature heat source/sink and/or reducing lost sensible heat in
the fluid and thermal storage vessels. Because the overall system
design can benefit from many small pressure ratio compressions, one
strategy would be to use a rotary compressor with a core similar to
a Wankel engine but with different volume ratios for each
successive rotor, potentially with multiple compression zones per
impeller rotation. Fluid compressed modestly per compression cycle
and per compression stage can be directed into a seawater-cooled
(or heated) heat exchanger. Fluid can then be directed through
another port into another section of the compressor.
[0060] As such, according to one embodiment, multiple stages share
a common shaft or multiple lobes within a rotary section of a C/E
that is configured to operate bi-directionally. The basic design
can be adjusted to different pressure ratios, specific to a unique
depth and storage pressure by adjusting clearances of the rotor and
cavity wall. Thus, because each installation of a system may have a
unique depth and storage pressure, a flexible design of a C/E can
save development cost while maximizing thermodynamic efficiency. As
such, referring to FIG. 6, a rotary Wankel C/E 200 having a center
shaft 202 and an eccentrically loaded rotor. Rotary Wankel C/E 200
includes an oblong cavity 206, and eccentrically loaded rotor 204
is positioned therein. Three cavities 207, 208, and 209 are formed
between eccentrically loaded rotor 204 and an outer housing 210. As
understood in the art, ports (not shown) may be coupled to regions
of the housing 210. The size and positioning of these ports and the
target output pressure determine the resulting pressure ratio for
these modest pressure ratio stage designs.
[0061] Some drive train designs can benefit from a clutch between a
motor/generator and a C/E according to embodiments of the
invention. A clutch offers some flexibility on how power can be
blended in the system. Mechanical power that drives the system,
such as a wind turbine or other RE power source, can be coupled to
the C/E via a clutch in order to selectively engage and disengage
the C/E. Thus, referring to FIG. 7, a system 300 much like system
10 illustrated above may include a prime mover or RE power source
302 such as a wind turbine or other RE devices as described. System
300 includes a generator/motor 304 coupled to RE power source 302
via a clutch 303, a clutch 306 coupling generator/motor 304 to a
C/E 308, a heat exchanger/pump combination 310, and a fluid
passageway (not illustrated) coupled to C/E 308 and configured to
be attached to a fluid storage device, such as flexible fluid bag
or fluid bag assembly 104 illustrated above. Also, although a
single passageway 312 is illustrated that couples heat
exchanger/pump combination 310 to C/E 308, it is to be understood
that multiple passageways 312 may be included, according to the
invention, enabling coolant to pass to interstage regions of a
multistage C/E. Thus, system 300 illustrates an RE power source 302
coupled to generator/motor 304, and if clutch 306 engages C/E 308
to generator/motor 304, then power can go into C/E 308 as well,
which, according to one embodiment, includes compressed fluid
passageways connected to the heat exchanger of heat exchanger/pump
combination 310. In such a fashion, RE power source 302 can
simultaneously generate electricity in generator/motor 304 while
also compressing fluid in C/E 308. In another mode of operation,
C/E 308 can be run in expansion mode to add power to
generator/motor 304 to augment power of RE power source 302. Clutch
306 allows C/E 308 to be decoupled from generator/motor 304 if
desired, depending on whether the current objective is to store
energy for the future, release stored energy, or neither of these.
The RE source 302 can also turn the generator but at a speed that
generally does not create or draw electrical power, putting most of
the energy into the CE, which compresses fluid for use later.
Another option (not shown) is to put a clutch between the RE source
302 and the Generator/Motor 304 to allow the CE and the
Generator/Motor to operate independent of the motion from 302. Yet
another option is to de-excite the field coils of such an
alternator/generator during compression, allowing nearly all of the
energy from prime mover power source 302 to pass through the clutch
306 to the C/E 308. Those of skill in the art would understand that
an alternator with field excitation comprises a form of electrical
generator in this context.
[0062] Embodiments of the invention have broader potential
application than underground CAES. It can be located offshore, in
proximity to nearly all major coastal population centers, and it
also can be located in lakes and reservoirs serving in proximity to
inland population centers. CAES systems typically include sites
with suitable geologic formations, which are often not available in
close proximity to many major load centers. Transmission line
congestion and capacity constraints make it impractical to locate
energy storage facilities long distances from load centers.
Therefore, underground CAES does not have the potential to provide
a ubiquitous solution to grid-scale energy storage needs.
[0063] Embodiments of the invention include design and operation
with existing marine RE systems that include but are not limited to
conventional wind power, hydro kinetic systems such as wave and
sub-sea turbines, and Ocean Thermal Energy Conversion (OTEC)
systems. However, in addition, embodiments of the invention include
standalone storage systems that can be remotely located in a marine
environment, which do not take advantage of existing RE
systems.
[0064] Further, in order to reduce or eliminate negative impacts of
RE systems, in one embodiment, bags are deployed to a benthic zone.
Typically, the benthic zone is an ecological region of a body of
water such as an ocean or lake having organisms that live therein
called benthos. Benthos generally live in close relationship with a
bottom or floor of a body of water, many of which permanently
attach to the bottom. The benthic region begins at a shoreline and
extends downward along a surface of the continental shelf. At the
continental shelf edge, typically approximately 200 meters deep, a
deepening gradient begins that is known as the continental slope
extending deep to the abyssal sea floor. Thus, according to
embodiments of the invention, it is desirable to deploy systems in
the benthic zone but at depths below which photosynthesis is
predominant, the marine life thereby being minimally impacted.
Materials of construction are generally non-toxic. Small fractions
of a sea floor may be dedicated to storage to provide substantial
amounts of storage capability over a larger area, while at the same
time leaving significant fractions of the seafloor as habitat for
the benthos.
[0065] The disclosed method and apparatus provides for computer
control to cause the system to store compressed fluid in an
underwater storage device and to extract energy therefrom.
[0066] One skilled in the art will appreciate that embodiments of
the invention may be interfaced to and controlled by a computer or
a computer readable storage medium having stored thereon a computer
program. The storage device comprises a computer readable storage
medium, which includes a plurality of components such as one or
more of electronic components, hardware components, and/or computer
software components. These components may include one or more
computer readable storage media that generally stores instructions
such as software, firmware and/or assembly language for performing
one or more portions of one or more implementations or embodiments
of a sequence. These computer readable storage media are generally
non-transitory and/or tangible. Examples of such a computer
readable storage medium include a recordable data storage medium of
a computer and/or storage device. The computer readable storage
media may employ, for example, one or more of a magnetic,
electrical, optical, biological, and/or atomic data storage medium.
Further, such media may take the form of, for example, floppy
disks, magnetic tapes, CD-ROMs, DVD-ROMs, hard disk drives, and/or
electronic memory. Other forms of non-transitory and/or tangible
computer readable storage media not list may be employed with
embodiments of the invention.
[0067] A number of such components can be combined or divided in an
implementation of a system. Further, such components may include a
set and/or series of computer instructions written in or
implemented with any of a number of programming languages, as will
be appreciated by those skilled in the art. In addition, other
forms of computer readable media such as a carrier wave may be
employed to embody a computer data signal representing a sequence
of instructions that when executed by one or more computers causes
the one or more computers to perform one or more portions of one or
more implementations or embodiments of a sequence.
[0068] According to one embodiment of the invention, a compressed
fluid storage system includes a bi-directional compressor/expander
(C/E) unit constructed to compress fluid during a first operational
mode and allow expansion of fluid in a second operational mode, a
fluid storage system positioned on a sea floor under a body of
water, and a piping system positioned between the C/E unit and the
fluid storage system and configured to pass fluid between the C/E
unit and the fluid storage system.
[0069] According to another embodiment of the invention, a method
of using a compressed fluid storage system, the method includes
applying rotational power to a shaft of a pressure conversion
device in a first rotational direction to compress fluid in a first
flow direction through the pressure conversion device, storing the
compressed fluid in a fluid storage system that is positioned
beneath a surface of a body of water, and passing the compressed
fluid from the fluid storage system through the pressure conversion
device in a second flow direction to apply rotational power to the
shaft in a second rotational direction, wherein the second flow
direction is opposite the first flow direction.
[0070] According to yet another embodiment of the invention, a
compressed fluid storage system includes a power source, a unitary
compressor/expander (C/E) device capable of both compressing and
expanding fluid coupled to the power source via a shaft and
comprising a plurality of compression/expansion (C/E) stages that
pressurize fluid in a compression mode and expand fluid in an
expansion mode, a fluid bag coupled to the plurality of
compression/expansion stages of the unitary C/E device and
positioned under a body of water, a pressured-fluid conveyance
system configured to pass pressurized fluid from the unitary C/E
device to the fluid bag when the unitary C/E device is in the
compression mode, and configured to pass the pressurized fluid from
the fluid bag to the unitary C/E device when the unitary C/E device
is in the expansion mode, and a control unit configured to invoke
the compression mode in the unitary C/E device, pressurize fluid
and direct the pressurized fluid to pass from the plurality of C/E
stages of the unitary C/E device to the fluid bag when power is
available from the power source, and invoke the expansion mode in
the unitary C/E device, direct the pressurized fluid to pass from
the fluid bag to the plurality of compression/expansion stages of
the unitary C/E device and expand the pressurized fluid when power
is selectively desired to be drawn from the fluid bag.
[0071] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
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